Why a Clear Stream Can Still Carry Giardia
Giardia is a microscopic parasite that can live in the intestines of people and animals. Its hardy resting form, called a cyst, can pass into feces and then reach streams through runoff or other contamination. Because cysts are far smaller than anything the eye can detect, a mountain stream can look pristine while carrying them.
What Happens After Someone Swallows It
If a person drinks water containing Giardia cysts, they can survive the trip through the stomach and become active in the small intestine. There, the parasites attach to the intestinal lining and multiply. The resulting illness, giardiasis, can cause diarrhea, cramps, nausea, bloating, and fatigue. Symptoms may not begin immediately, so a camper might not connect feeling sick days later with a drink taken on the trail.
An infected person can shed more cysts in stool, helping the parasite spread when sanitation is poor. That makes careful waste disposal important around campsites, especially near water sources.
Appearance Is Not a Safety Test
Clarity shows that water contains little visible sediment; it does not reveal microscopic contamination. Water may also carry other disease-causing organisms that cannot be seen. A clear stream is a view, not a test. Treating water with a method effective against parasites—such as boiling or an appropriately rated filter—helps reduce the risk before drinking it.
